To experience Mumbai in a day, it is best not to do too much advance planning. Creating a detailed itinerary in a city that is so spontaneous, so elusive and unpredictable, is risky business. Better to just plunge in, as if it were an ice-cold lake on a hot summer day. But don’t expect the same relief. Not only is Mumbai’s average high temperature 93 degrees year-round, but monstrous traffic jams, street noise, crowded sidewalks and monsoon flooding can make a day in the city more work than play, though also an amazing travel experience.

This city of about 14 million residents wakes before dawn, with filled-to-capacity electric commuter trains gliding into Mumbai’s rail stations as a brilliant fuchsia sky spreads across the horizon, bathing everything under it — serene Hindu temples, Marine Drive as it curves along the beach, street vendor carts, rickshaws, the Muslim Haji Ali Mosque floating like a mirage off the coast — with a beautiful and surreal glow.

Start the day at dawn either at Sassoon Dock in the south end of the Colaba district, where colorfully dressed Koli women sort the catch from the early-morning fishing boats, or at the Dadar Flower Market, under the overpass by Dadar Station. Here, sweet-smelling white jasmine blossoms, chains of rose petals and hundreds of other flowers are brought in from the countryside at 5:30 each morning, a nice adornment for your female traveling companion’s hair.

Visit Apollo Bunder, where the iconic Gateway of India looks out to Mumbai Harbour. This area is popular with tourists and diverse groups of locals, a lively and colorful scene that is sometimes called the “Crossroads of India.” Walk to MG Road, where the National Gallery of Modern Art and Jehangir Art Gallery are located. Then grab a vada pav for lunch from a street vendor. These ubiquitous veggie burgers (few Mumbaikars eat pork or beef), seasoned potato patties served on a bun with mint and tamarind chutney sauce, are as common as the hamburger in the United States.

In the afternoon, when the temperature and humidity reach their peak, retreat to your air-conditioned hotel room for a short nap or get a rose petal powder and ashwagandha milk bath at the JW Marriott’s Quan Spa (Juhu Tara Road, tel 91 22 6693 3000). Afterward, join a Reality Tours group for a visit to Dharavi, a poor and bustling neighborhood in central Mumbai where Slumdog Millionaire was filmed. The district has a million residents, narrow lanes and small-scale industries — all of it now being eyed by real estate moguls who want to develop its 535 city-center acres.

With twilight approaching, hop on a double-decker city bus, 3 rupees a ticket ($.06), which runs on limited routes in South Mumbai. Try for a front seat on the upper level for great views of the swirling humanity passing before you. At dusk, when the lingering heat is tempered by cool drinks served on dramatic rooftop bars high above the city, visit Aer (14 Dr. E. Moses Road, Worli), the 34th-floor lounge at the Four Seasons Hotel. From the vantage point of India’s highest outdoor bar you will have a 360-degree view of Mumbai. As the sky darkens and the lights of the city are switched on, illuminating the historic, grand colonial-era buildings and thousands of street-side food stalls, Mumbai will look and feel magical.